Two-way trunk circuit arranged for dial-back operations



Feb. 26, 1952 s. w. ALLISON TWO-WAY TRUNK CIRCUIT ARRANGED FOR DIAL-BACK OPERATIONS Filed July 24. 1948 4 Sheets-Sheet l ow ASHES M295 INVENTOR S. W ALL/SON ma ma ATTORNEY Feb. 26, 1952 s. w. ALLISON 2,

TWO-WAY TRUNK CIRCUIT ARRANGED FOR DIAL-BACK OPERATIONS Filed July 24, 1948 4 Sheets-Sheet 2 FIG. 2

INVENTOI? S. M. ALL/SON A T ZOPNEV Feb. 26, 1952 s. w. ALLISON TWO-WAY TRUNK CIRCUIT ARRANGED FOR DIAL-BACK OPERATIONS 4 Sheets-Sheet 5 Filed July 24, 1948 lml MS \WQ A T T R Y TRUNK CIRCUIT I50 Feb. 26, 1952 s. w. ALLISON 2,585,901

TWO-WAY TRUNK CIRCUIT ARRANGED FOR DIAL-BACK OPERATIONS Filed July 24, 1948 4 Sheets$heet 4 INVENTOR .5. W. ALL/SON ATTORNEY Patented Feb. 26, 1952 UNITED STATES PATENT OFFICE TWO -WAY TRUNK CIRCUIT ARRANGED FOR DIAL-BACK OPERATIONS Sewell W. Allison,.West Orange, N. J., assignor to Bell-"Telephone Laboratories,*- Incorporated,- New York, N.-'YJ, a-corporationof New York- ApplicationJuly 24, 1948,:Serial No. 40,384

4 Claims. 1

This invention relates to telephone systems and particularly to telephone systems comprising community dial ofiices and an operator oifice.

Objects of the invention are an increased chi-'- clency in the handlin and completion by an operator of calls between community dial 'offices, only one of which has direct trunks to an operator office, and the provision of improved circuit'ar rangements at the operator oflice for use in completing such calls.

In systems comprising a, plurality of community dial ofiices, one of which has direct trunks to an operator office, calls between dial offic'es are first extended to an operator and completion of these calls is effected by the so-called dial-back method wherein the same trunk used in extending acall to the operator is used by the operator to complete the call. The operator may 'b'eprovided with a dial for use in directly controlling switches in the intermediate and terminating dial ofiices or may be provided with a key set in which case, the digits keyed by the operator are first registered in a register sender and the sender then transmits impulses which are repeated over the trunk to control completion of the described connection. If any of these or other dial oflices", to which the sender is adapted to route calls, are arranged to transmit a stop-dial signal until the equipment therein is ready to receive trains of digit impulses and to then transmit a start dia'l signal to the operator, the stop-dial signal condition exists when an operator answers a call in coming from a dial ofiice. Furthermore, in order to condition the trunk circuit in the dial ofiice for the control-of switches responsive'to' digitimpulses incoming over the trunk used in extending a call to an operator, it has been necessary for the operator to dial a prefix digit followed by the digits which operate the switches through which the desired connection is completed.

This invention is the provision of a trunk circuit, associated in an operator office with a trunk from a dial office, arranged for dial-back operation to complete calls between dial ofiic'es'and arranged to simulate a start-dial signal on'a dialback call to enable the transmission of impulses from an associated register sender over the trunk to the dial oifice while a stop-dial signal is being received over the trunk.

A feature of the invention is the provision of a trunk circuit, associated in an operator ofilc'e' with a trunk from a dial office, arranged for dial-back operation to complete calls between dial oflices and arranged to automatically transmit a. prefix digit to prepare the dial ofiice switches for re 2 sponse" to trains of impulses corresponding to the directorynumber, so that the operator dials or keysthesame directory number digits on al-lcalls overthe'trunkand does not needto dial or key a prefix digit on a dial-back call since the prefix.

digit is automatically transmitted.

To facilitate a clear and complete understand ing of the invention, a telephone system comprising dial and operator ofiices and trunk circuits embodying .theinvention andits featuresis shown schematically in the drawing; Reierringto the drawing:

Fig. 1 shows threedial ofiices A, B and C, the office A being provided'with trunks to each of offices Band C and with trunks to a master oifice;

Figs; 1, 2 and 3 show a trunk circuit 40 associated with" a two-waytrunk Tl interconnecting dial ofii'ceA'and' a toll oflice, the trunk Tl being arranged for composite signaling;

Fig. 4shows a trunk circuit I50,-a cord I90, and operator position equipment I95 andkey set I96;

Fig.4A shows a modification of trunk circuit l5llwhich may be-applied at line A-A in Fig. 4 to arrange this trunk circuit to automatically transmit a prefix digit when a cord is connected to-the dial-back-jack' DBJ and Figi'fi 'shows the'relative positions in which Figs. 1' to 4' are-tube placed to forman'operative arrangement.

Each of the dial offices A, B and-C includes line finder," selector and connector switches of the well-known two-motion step-by-step type. The subscriber stations are of the common battery type and include dials for controlling the selector and connector switches to complete desired connections. The subscriber lines terminate in the banks of'-line-finder switches which operate to connect calling lines to selector switches and also terminate in the banks ofconnector switches which select called lines. The lines are two-wire lines although represented bya single conductor. Each of the switches comprises a set of brushes and a bank of terminals and is represented in the drawin by a single brush and'two or three terminals. Reference may be had to Automatic Telephony by Smith and Campbell, 2nd edition, pages 53 to for a description of the structure of two-'n-rotionstep-by -step switches and their operationwhe'nused as selectors and connectors. R'eferencemay be had to Patent 1,799,654 granted April 7, 1931, to R. L. Stokely for description of the operation'of a two-motion step-by-step line finder.

In"dial oflice A, subscriber stations [I and I2 are" connected td'terminals in the banks of line finders I3 and to terminals in the banks of connectors. I5. The line finder I3 is associated with a first selector I4, which has access to groups of connectors, one of which includes connector I5; and also has access to a group of trunks such as TI extending to the toll ofiice. In dial office B, stations 2| and 22 are connected to terminals in the bands of line finders 23 and connectors and first selectors 24 have access to connectors 25 and also to trunks 26 to dial oifice A. In dial oifice C, stations 3I and 32 are connected to terminals in the banks of line finders 33 and connec tors and first selectors 34 have access to connectors 35 and also to trunks 36 to dial ofi'lce A. The trunks 20 and 36 from ofiices B and C terminate at ofiice A in trunk hunting switches 29 and 39, each of which has access to the trunks TI extending to the toll ofiice. The switches 29 and 39 may be of the rotary step-by-step type shown in Fig. 4 and described in Patent 2,233,282 granted February 25, 1941 to R. B. Buchanan and C. D. Koechling. Calls between subscribers in any one of ofiices A, B or C are completed by the switches in that ofiice, but calls originating in any one of these ofiices and terminating in any other ofiice are routed to the toll office and are completed under the control of an operator. The trunks between dial oifice A and the toll ofiice may, like trunk TI, be arranged for composite signaling. The trunk circuit 40, to which the trunk TI is connected in dial ofiice A, has associated therewith two selectors 60 and 1 0 each of which has access to trunks I8 extending to connectors I5 in oflice A, to trunks 28 extending to incoming selectors 21 in ofiice B, and to trunks 38 extending to incoming selectors 31 in office C. The trunk circuit is arranged so that selector 10 is controlled by digit impulses incoming over trunk TI on toll calls to called stations in any one of the dial offices both on calls originating in offices other than dial oifices A, B or C and on delayed calls between stations in difierent ones of ofiices A, B and C. On calls originating in one of oifices A, B or C and terminating in another of these ofiices which can be completed without delay by dialing back over the trunk TI, a prefix digit is received over trunk TI to enable the operation of selector 60, the first digit following the prefix digit being efiective to control the operation of selector 60. When completing delayed calls over trunk TI between subscribers in different ones of ofiices A, B and C, an operator in the toll ofiice first extends a connection which includes selector 10 to the called subscriber sta tion, a prefix digit is then transmitted over trunk TI to prepare the trunk circuit 40 to control selector B0, and the first digit following the prefix digit controls the operation of selector 60.

The toll ofiice comprises a plurality of operator positions including positions at which the trunks TI from dial office A are terminated. The trunk circuit I associated with trunk TI in the toll office includes answering, outgoing and dial-back jacks designated AJ, OJ and DBJ, respectively. The operator position includes cords I90 and a key set I96 for use in extending calls over trunks TI to subscribers stations in offices A, B

and C. Reference may be had to Patent 2,276,515 granted July 4, 1933 to T. D. Robb for disclosure of an operator position and to Patent 1,916,760 granted July 4, 1933 to I. H. Henry and Patent 2,167,710 granted August 1, 1939 to T. F. Crocker for key set, sender and link circuits. The trunk circuit I50 as shown in Fig. 4 is arranged so that it is necessary for the operator to key the prefix digit on dial-back and delayed dial-back calls over trunk TI. If trunk circuit I50 is modified by the substitution of Fig. 4A on line A-A, insertion of a plug in the dial-back jack DBJ automatically effects the transmission of a prefix digit so that the operator may in all cases key the same directory number digits to establish desired connections with calling and called stations in any one of dial oifices A, B and C.

Call from dial ofi'ice A to toll ojfice Assume now that a call is initiated at the subscribers station II in dial office A; that the call is extended through a line-finder switch I3 to a first selector switch I4, and that the selector I4 is operated under the control of a train of A dial impulses from the calling station to select an idle trunk circuit 40 associated with the trunk TI which extends to the toll oifice. Upon selection of trunk circuit 40, the windings of relay 9'! are connected through conductors 65 and 66, back contacts of relay 64, conductors 41 and 48, left windings of repeating coil 50, conductors 45 and 46, back contacts of relay 44, conductors M and 42, and through brushes of selector I4 and line-finder I3 to the calling station II. The operation of relay 91 closes a connection from the ringing tone source 11, through condenser 18, a back contact of relay 80, conductor 99, a front contact of relay 91 and conductor 98, to conductor 45; whereby ringing tone is transmitted to station II to indicate that an operator is being signaled. Relay 91 also closes a circuit for operating relay 9B and a circuit including the right back contact of relay 90 for operating relay I25. The operation of relay 96 connects ground to conductor 43 to hold the selector and line-finder switches I4 and I3 in operated position; and opens the normallyclosed, id1eindicating connection from battery through the lower winding and a backcontact of relay 64, conductor 69 and a back contact of relay 96, to sleeve conductor 43, thereby marking the trunk circuit 40 busy in the banks of switches having access thereto. The operation of relay I25 disconnects ground from signaling conductor I31 and connects signaling battery through lamp I26 to conductor I31 to cause the operation of the composite signaling relay I45 in the toll office. The operation of relay I45 connects ground to incoming signaling conductor I49, thence through the upper back contact of relay I15 and a back contact of relay I80, to the winding of relay I19 of trunk circuit I50. The operation of relay I19 closes a circuit for operating relay I86, closes a circuit including a back contact of relay I for lighting the answering lamp I54, and bridges the talk ing condenser I43 across the inner ends of the right windings of repeating coil I40. The operation of relay I86 connects battery through resistor I84, a back contact and lower winding of relay I83 to the sleeve conductor I53 of answering jack AJ and the associated outgoing jacks (not shown) to establish a busy marking condition at the outgoing jacks. In case the trunk circuit I50 is also accessible to selectors of an intertoll train, this busy marking potential is further connected to the test terminal in the banks of the selectors.

When a toll operator answers the call by inserting the plug I9I Of a cord I90 in answering in the position circuit I95.

bridges talking condenser jack AJ, a circuit is closed for operatively ener izing the upper winding of relay I83. When the plug is fully seated, a circuit is closed for operating relay I80, this circuit including the winding and continuity backcontact of relay I80, a back contact of relay I54, a back contactof relay I63, tip conductors of jack AJ and plug I9I, .to ground Relay I80 closes a locking circuit which is under control of .relay I83, opens its own operating circuit, .closes :-a locking circuit for relay I19 whichyincludesa back contact of relay IBI, opens the circuit :for lighting the answering lamp I54, and transfers the Outgoing signaling conductor I41 from ground to signaling battery, theconnection-between conductor It? and the transfer contact spring of relay I89 being traced througha back contact of relay I85 andstheinner lower front contact of relay I19. The connection of signaling battery to conductor I47 causes theoperation of the composite signaling relay I35 in dial ofiice A. The circuit for operatively energizing the middle and lower windings of relay I35 is further traced from conductor I47, through retard coil I45, middle winding of relay I45, lowerwindings of coils I44, lower conductor of trunk T I, lower windings of coils I34, middle and lowerwindings of relay I35 and biasing battery to ground in dial oifice A. The operation of relay I35 connects ground to conductor [-39, thereby causing the operation of relay II9 of trunk circuit 49. lhe

operation of relay I I9 closes a circuit for operating relay H5. The operation of relay H closes circuits for operating relays IIII and [H .and I33 across the left windings of repeating coil I30. The operation of relay I II] connectsground to conductors 63 and H2; closes a locking circuit for relay 96; and closes a circuit for operatively energizing the left winding of relay -89, this circuit including the left-winding and outer left back contact of relay 8D; conductor I I3, inner right front contact of relay I II? to ground at the outer right front contact of relay 9?. The operation of relay-80 first closes a locking circuit through its right winding and inner right front contact, over conductor II2 to ground'at a front contact of relay I III; then opens the operating circuit through its left Winding and closes a circuit including conductors II3 and-83 for operating relay I04; closes a circuit including conductor I It for operating relay I I'Iyand opens the connection between ringing tone source I? and conductor 45 to terminate the transmission of ringing tone-to the calling station I I. Relay I04 locks to conductor 63 independentof relay 80 and bridges the talking condenser I23 across the right-hand windings of repeating coil 50. 'The operation of relay I I1 closes a circuit foroperating relay I56. Relay I96 looks through a front contact-of relay H5 and conductor I I4 toground at a front contact of relay S0. The operation of 'relay I56 causes the release of relay H1; and the release of relay III opens the operating circuit of relay I06 and closes a circuit including conductor I9! for operating relay 44. The operation of relay 44 interchanges the connection between conductors M and 42 and the windings of relay 9] thereby reversing the current in theloop circuit including the calling station I I.

The toll operator now receives the called office code and number from the calling subscriber;

.and, if the connection is to be completed over an outgoing trunk, the plug I92 is connected to an outgoing trunk jack associated with a trunk (not shown)- leading to. thecalled ,ofilce. Talking bat- ,tery is; supplied to the, calling station througlrthe windings of relayg-B'I and the .left windings :of repeating coil 50-andrthe talkingconnection be tween the callingsubscriber. and .thecord I95 includes repeating ;-coil I30, the conductors of trunk TI, repeatingcoil I40, conductors I55 and I55, back contactsofrelays I64 and I 53, conductors I5I and I52 and :thetip and ring conductors of jack AJ and plug I9I. The calling subscriber may'fiash the toll cord supervisory lamp I93 by switchhook operations which cause the alternate release and reoperation of relays 9'! and I25 in. succession. The alternate release and reoperation of relay I25 causes the transfer of signaling conductorIS'I from signaling battery to ground and back'to signaling battery, thereby effecting the releaseand reoperation of the composite signaling relay I45 in the toll office. Each time relay'I45 releases, ground is connected to conductor I48, thence through a back contact of relay I15 and a front contact of relay 89 to the low-resistance, lower winding of relay I23 thereby increasing the current through the sleeve conductor of plug I9I to light lamp I93; and when relay I45 reoperates, ground is disconnected from conductor I48 to extinguish lamp I93.

When the calling subscriber replaces the receiver on the receiver hook to terminate the call, the release of relays 97 and I25 causes the release of relay I45 and lamp I93 is lighted as a disconnect signal. When the toll operator disconnects plug Iti from jack AJ, lamp I93 is extinguished and relay I83re1eases. The release of relay I83 causes the release of relay I85; and the release of relay I89 causes the-release of relay I19. With relays I79 and I89 released, the signaling conductor I4! is disconnected from signaling battery and connected to ground, thereby causing the release of composite signaling relay I35 in dial office A. Therelease of relay I35 causes the release of relay II9. The release of relay II9 causes the operation of relay I24 and the release of relay H5. The operation of relay I24 causes the release'of relay I2I. The release of relay II5 causes the release of relays H9 and I24 and opens the bridge across the left windings of repeating coil I39. The release of relay III causes the release of relays 95, I54 and I56. The release of relay' I96 causes the release of relay 44; and the release of relay causes the release of relay 80 and reconnects battery through the lower winding of relay 54 to sleeve conductor 43, thereby to mark the trunk circuit '45 as idle in the banks of all selectors having terminals connected to thetrunk circuit 49.

Call from dial 017106 A to dial ofiice B Assume next that the subscriber at staticn II originates a call which is extended overtrunk TI to the toll operator and answered by connection of a plug I9I to jack AJ, and that the called station is a station 22 in dial office B. In this case, the call is completed by dialing back over trunk .TI to selectively operate the selector 69 associated with trunk circuit 45 to select an idle trunk terminating in an incoming selector in dial ofiice B, and to selectively operate this incoming selector and a connector to establish connection with the line of the called station. While the dial-back operation may be directly effected by a position dial, the trunk circuit and operator position shown in Fig. 4 are arranged for key set operation and in this case the digit signals are first registered in a register sender der control of the sender, over trunk TI. The toll operator connects the plug I92 of cord I90 in the dial-back jack DBJ, thereby closing a circuit through the sleeve-conductor of plug I92 for operating relay I53. The operation of relay I83 opens the connection between conductors I55 and I50 and jack AJ, and connects the incoming signaling conductor I49 through a back contact of relay I52 to the winding of relay IGI. Since relay I45 is operated at this time, conductor I49 is connected to ground and relay IBI operates. Relay IBI locks to conductor I49, independent of relay I52, opens the locking circuit of relay I10 causing this relay to release, and opens the connection between conductors 208 and 201 thereby to prevent the operation of relay I11 when a sender is connected to trunk circuit I50. With relay I80 operated and relay I19 released, the link start conductor I50 is connected through a back contact of relay I19 and a back contact of relay I85 to ground at a front contact of relay I80 to cause the operation of a link circuit to effect the connection of an idle sender to. the trunk circuit I55. When a link I68 connects with trunk circuit I55, ground is connected in the link to conductor I51 thence through a front contact of relay I80 and a back contact of relay I19 to the winding of relay I85. Relay I85 operates and locks to conductor I61 independent of relay I19. When an idle sender is associated with trunk circuit I50, battery in the link is connected through conductor I69 to the winding of relay I54. Relay IE4 operates, disconnecting conductors I55 and I56 from jack DBJ and establishing a connection from the key set I95 through tip and ring conductors of plug I9I and jack DBJ, conductors I51 and I58, front contacts of relay I54, conductors I55 and IE5 and link circuit I68 to the sender I; and when the digits of the called line number are keyed by the operator, key set impulses are transmitted over conductors I55 and IE6 to register the keyed digits in the sender I10. The operation of relay IBIS connects ground to register I88 so that resistor IE8 is in parallel with the winding of relay I01; and closes a circuit for operating relay I15. Relay I looks under control of relays I and I83, closes a circuit from battery through the lowermost back contact of relay I19 and resistor I15 for operating relay I81, and closes a circuit including a front contact of relay I53 for operating relay I52. Although relay I is operated so that conductor I49 is connected to ground, the operation of relay I15 is ineffective to operate relay I11 due to the fact that the connection between conductors 255 and 201 is opened by the operation of relay Hill. The operation of relay I81 connects signaling battery to the outgoing signaling conductor I41 independent of relays I19 and I80. Relay I52 locks independent of relay I15 under the joint control of relays I53 and I80. The operation of relay I62 opens the operating circuit of relay IBI and closes a circuit for operating relay I19 this circuit being traced from ground at the outer upper front contact of relay I52, through a front contact of relay I5I, conductor I48, outer lower front con tact of relay I15, continuity contact and winding of relay I19 to battery. Relay I19 opens its operating circuit after closing a locking circuit which includes the inner lower front contact of relay I62, conductor I99 and a front contact of relay I80. The operation of relay I19 disconnects ground from the link start conductor I; closes an additional ground connection for the locking circuit of relay I52; opens the connection which includes a front contact of relay I between the signaling battery and the outgoing signaling conductor I41 so that the connection of signaling battery and ground to conductor I41 is under the sole control of relay I81; opens the circuit through resistor I16 and winding of relay I81; and closes a circuit for energizing relay I81 under the control of an impulse transmitting relay (not shown) in the sender I10. The last-mentioned circuit is traced from battery through resistor I18, a back contact of relay I11, a front contact of relay I15, conductor I13, through the link, through sender I10 including the winding of polarized relay I1I, conductor I14, a front contact of relay I15, a from contact of relay I19, a back contact of relay I11, and through the winding of relay I81 to ground. The impulse transmitting relay of the sender is thus rendered effective to transmit trains of. impulses in this circuit to relay I81. and these impulses are repeated by relay I81 over conductor I41 and lower conductor of trunk TI to control the composite signaling relay I35. The digits thus transmitted consist of a prefix digit which prepares the trunk circuit 49 for control of selector 50 followed by one digit for operating this selector and digits for operating an incoming selector 21 and a connector 25 in the called ofiice B.

When relay I35 receives the digit impulses from the toll office, it repeats these impulses to relay II9. Each impulse causes the release and reoperation of relay H9, the release of relay II9 responsive to the first impulse of each train being effective to operate relay I24. Relay I24 is slow to release and remains operated during receipt of each train of impulses and releases only during the intervals between digits. Relay H5 is also slow in releasing and remains operated during the response of relay II9 to digit impulses. The operation of relay I24 opens the circuit for energizing the winding of relay I2 I; and the prefix digit train of impulses will consist of enough impulses to cause the release of relay I2I. The release of relay 'I2I closes a circuit from battery through the lower winding and a back contact of relay 51, conductor 53, a front contact of relay I04, a front contact of relay I06, back contact of relay I2I, outer right front contact of relay I24, to ground at the left front contact of relay I15. Relay 51 is thus energized sufficiently to close its upper locking contact, the upper winding of relay 51 being short-circuited as long as relay I24 remains operated. When relay II9 remains operated after the last impulse of the prefix digit, relay I24 releases thereby opening the short circuit across the upper winding of relay 51; whereupon relay 51 is completely operated by the energization of both windings in series, through the locking and contact and conductor 59 to ground at a front contact of relay H5. The complete operation of relay 51 closes a circuit for operating relay 90, this circuit being traced from the winding of relay through its continuity back contact, conductor 9|, inner lower front contact of relay 51, conductor I05, a front contact of relay I04, to ground at a front contact of relay IIO. Relay 90 locks through its continuity front contact directly to the contact of relay IIO, bridges condenser 55 across the inner ends of the left windings of repeating coil 50, causes the release of relay I25, closes a circuit including conductor 94 for energizing the right winding of relay 86, and. closes a bridge across the tip and ring contheouter uppenfront-contactofirelay 51,- upper.

rightwinding of repeating,coil 50,,left windingv of relay 86, conductor 81, outer leftgfrontcone tact ofrelay 90, resistor 95,- outerleftefrontcontact .of relay I04, right front contact. of, relay, I I9, a right front .contact of relay. I04, conductor 53, lower right winding .of repeating rcoil 50,- and through another. front. contact .of. relay. 51 to conductor 52. Relay 85 does nct.operate-since its. windings are. differentially energizedi at this.

to relay I I9. The aforementioned-release.ofree lay. I25, .when.relay SILoperates, connects ground to signalingconductor I31. in plaoeof signaling battery thus causing thereleaseof, relays.- I45. and I 6I in the toll .oflice. The releaseofrelay. IB'I- places the back contactofrelay I 45.in.control of .the operators cord supervisory lamp. I 93.after relay I releases.

The impulses .of the first .train received by relay I and repeated to relay II9, ,following'the operation of relay 80, are repeated by relay II9 over conductors 6| and. 62 to selectively operate selector 60 to selecta levelin whichthe terminals are'connected to.trunks.to the called dialoffice B. Theselector 60 thus'selects an idle trunkv 28 and" the following trains of impulses are received by relay I35 and repeated by relay II9. overconductors BI and 62 andv trunk'28 to op erate the associated incomingselector 21 and a: connector 25 to complete the connectionto the lineof the called station "22. After thesender I19 is through transmitting trains. of impulses to relay I81, ground is disconnected from conductor I61 thereby causing'the release'of relay I85 of trunk circuit I50. The release of'relay I85 again places the outgoing signaling"conduc tor I41 under the control of relay'I8D. A short interval after relay I85 releases, the connection of battery to conductor IE9 is openedin the link and relay I64 releases. The release of relay I64 causes the release of relay I15; disconnects conductors I65 and I 66 from dial'jack DBJ; and connects conductors I55 and I56 .to dial jack DBJ so that there is a talking connection between the called station and. the toll operator, if the'plug I92 is not immediately disconnected from jack DBJ after keying is completed. The

release of relay I15 disconnects conductors I13.

the back contact of relay 91, conductor 85, a.

front contact of relay 80, back contacts of.relays 89 and 86, and conductor 93, .tolgroundat a front contact of relay 99. The operation and release of relay I45, after relayv I6I has released; disconnects and .reconnects. ground .to the lower.

low resistance Winding of relay I83 thereby flash,- ing lamp I93. Theplug I92 may bEdiSCOIlr. nected from jack DBJ assoon, as keying, of the digits is.completed. When .plug. I 92'isdis: connected from jack DBJ 're1aysI63 and 1621 case:

If and when thecalled subscriber. answers, the current isreversed through the conductors of trunk 28 and through .thebridge across conductors GI and 62, thereby causing the energization of the left winding of relay 8% to aid the right winding, so that relay 86 operates. The operation of relay 86 closes a circuit including conductor 53 for operating relay 89; and closes a circuit including conductors 92 and 93 and. front contacts of relays 98 and 91 for operating relay 25. The

.operationof relay I25 reconnects signaling battery to conductor I31 to again operate relay H55 in the toll oflice and thus cause the supervisory lamp I93 to be extinguished. The talking connection betwen the calling station II in dial office A and the called station 22 in dial office B includes repeating coil 58. Either the calling or called subscriber may flash the operator, relay 91 being controlled by the calling station I I and relay 86 being controlled by the called station 22 and the release and reoperation of either of relays 91 and 86 causes the release and reoperation of. relay 25 to transmit a signal over the composite signaling circuit and thus effect the fiashingof supervisory lamp I93 of cord I98. The

connection is held-under the control of the toll operator. When plug ISI ofcordiSll is disconnectedfrom jackAJ, relays I83, I89 and I19 releasein succession. With both ofrelays I19 and I 89. released, relay minating thev busy marking of the outgoing jacks to. which trunk. IE8 is connected; and signaling conductor M1 is again connected throughback contacts of. relays I19 and ISO. to ground, thus i causing the release of relaysI35 and I I9-in dial office A. The release-cf relay I Iii-causes the opera-- the release of relay I96 causes'the release of relay 4-4; and the release ofrelay 96causes the release of .relay 88 and disconnects ground from conductor 43. Whenholding ground is disconnected from, conductor43, the selector I4-and line finder I 3 arereleased. and restoredto normal.

Assumenext that a toll operator. answers a call with plug I9I.of cord lililandthat thecall is one which is tobe completed over a trunk between the toll Mice and dial oflice A.. Many of the circuit operations are similar to those hereinbefore, described and will notrequire a r detailed tracing,of.the circuits. Whenthe plug I 92-is connected/to jack. OJ, acircuitis closed-through the. sleeve conductor of the plugand jackfor operating relay I83 and acircuit is closed through the..tip conductor of the plug-and jack for opera- I ting relay I80. Relay. I88 locks under control'of relay I83; .closesa circuit foroperating relay I; transferssignaling conductor I41-from ground to signalingbattery, to operate relay I35 in the'clial ofliceA; connects ground toconductor I68 to effect the operation of a-link, whereby an idle sender I1Ilis connectedthroughthelinkto the trunk circuit- I 50..as .hereinbefore described; and" closes a connectionfromgrcund at-the middleupper back I86 releases, thereby ter-- contact of relay I19 and a back contact of relay 54 to the lower, low-resistance winding of relay 183, thereby to efiect the lighting of cord supervisory lamp 194. When a link connects with trunk circuit 1511, relay I85 operates; and, when an idle sender is connected to trunk 15 0, relays I64 and 115 are operated. The operation of relay I15 closes a circuit for operating relay 119, this circuit including conductor I48 and the back contact of composite signaling relay I45. The operation of relay 115 also connects the winding of relay 111 to conductor 149 so that a stop-dial signal incoming to relay 145 will cause the operation of relay I11 and thus reverse the current through conductors I13 and 114 to operate relay I H and thereby prevent the transmission of digit impulses to relay 181. With relays I64, I15, I19, I00, I33 and I85 operated, the sender is ready to register the digits keyed by the operator; and relay 181 is connected for operation under the control of the impulse transmitting relay in the sender.

When signaling battery is connected to conductor I41, responsive to seizure of trunk circuit I50, the operation of composite signaling relay 135 in dial ofiice A closes the circuit for operating relay I19; and relay I19 closes the circuit for operating relay I15. The operation of relay I15 bridges condenser I33 across the left windings of repeating coil I30, and connects ground to condoctor 59 to operate relays I10 and 121. The operation of relay I10 connects ground to sleeve conductor 63 of selector 60 and connects ground through conductor I I2 and a back contact of relay 96 to sleeve conductor 13 of selector 10, to the upper winding of relay 64, and to the right winding of relay I 00. Relay 54 operates, opens the connection between the lower winding of relay 64 and conductor 43, and connects ground through conductor 69, and a back contact of relay 96 to conductor 43, thereby to guard against seizure of trunk circuit 40 by any of selectors 14 or trunk hunting switches 29 and 39. The operation of relay 64 disconnects the windings of relay 91 from the left windings of repeating coil 50 and closes a bridge including the left windings of repeating coil 50, conductors I51 and 68, the left winding of relay 100, back contacts of relay I04 and the right front contact of relay I19 across the tip and ring conductors 11 and 12 of selector 10, thereby preparing selector 10 for operation responsive to digit impulses received by relay I 35 and repeated to relay I19. Relay I does not operate at this time due to the fact that its windings are energized in opposing directions.

When the operator keys the particular digits reouired for completing the call, these digits are registered in the sender and relay I81 is operated under the control of the impulse transmitting relay in the sender to transmit trains of impulses corresponding to these digits over trunk TI to the composite signaling relay I35; and relay I35 repeats these impulses to relay I19. Relay I24 is operated by the release of relay I19 responsive to the first impulse of each digit train and remains operated until all of the impulses of a train have been received by relay 119. The selector is selectively operated responsive to the first train of impulses repeated by relay 119 to select a trunk 18 which extends to a connector if the line of the called station terminates in dial oilice A, to select an idle trunk 28 which extends to an incoming selector 21 in dial oflice B if the line of the called station terminates in dial ofiice B, or to select a trunk 33 3:

12 tends to an incoming selector 31 in dial ofiiceq if the line of the called station terminates in dial ofilce C. In each case, the succeeding trains of impulses effect the completion of the connection between the toll ofiice and the called line. When the call is answered, the reversal of current over conductors 1i and 12 causes the operation of talking connection between the called station and trunk TI includes repeating coils 50 and I30. When the called subscriber replaces the receiver on the receiver hook, the current through conductors 11 and 12 is again reversed causing the release of relays I00 and 125 in succession. The release of relay I25 disconnects signaling battery and reconnects ground to conductor I31 causing the release of signaling relay I45 in the toll ofllce; and the release of relay I45 causes the lamp I94 to light as a disconnect signal. When the operator disconnects from jack OJ, relays I83, I and 119 are released in succession, and the outgoing signaling conductor I 41 is disconnected from signaling battery and reconnected to ground, causing the release of composite signaling relay I45 in dial oflice A. The release of relay 145 causes the successive release of relays I19, II5, H0 and 104. The release of relay 119 also opens the bridge across conductors 11 and 12 to effect the release and return to normal of the selector and connector switches through which connection with the called line was established. The release of relay also causes the releaseof relay 04, the trunk circuit 00 thus being restored to normal, ready for use on another call.

Delayed calls between dial ojfices When a subscriber in any one of the dial oflices calls a subscriber station in another one of these ofiices and the call cannot be immediately completed, it may be completed later by an operator in the toll office. In this case, the operator connects one plug of a cord 190 with an outgoing jack OJ and extends the connection to the called line in the same manner as above described on a call incoming from another toll ofiice. After the called subscriber answers, the operator asks the subscriber to wait until connection is established to the calling subscriber. T0 effect this connection, the operator connects the other end of cord I90 to the dial-back jack DBJ, causing the operation of relay I63. Relay I63 disconnects the tip and ring conductors of jack OJ from the tip and ring conductors of jack DBJ to prevent interference with key pulsing, and closes a circuit for operating relay I61. Relay I61 locks independent of relay I62 and opens the lockin circuit of relay I19. Relay I19 releases thereby connecting ground to the link start conductor 160. When a link I68 connects with trunk circuit 150, relay I85 is operated, and when an idle sender is con-- nected through the link to trunk circuit I50, re lays I64 and operate in succession. The operation of relay I15 closes a circuit for operating relay I62. Relay I62 locks under control of relay I63, opens the operating circuit of relay I61, and

'13 connects 'ground 'to conductor I48'to reoperate relay' l'l9. Whenrelay I19 operates, the key "pulsing circuits are-completedfrom the key set I955,

through cord I99, jack DBJ, front contacts of is lay'lfid and conductors Hi and Q96; and the keying of "the digits required for completing a connection to the calling station effects the registra tion of these digits in the sender. The sender then controls relay I81 to transmit the registered digits over trunk TI to the composite signaling relay I in dial ofiice A in the manner hereinbefore describedj andthe digit impulses are repeated by relay I35 'torelay I I9; The first digit is a prefix digit which consists of a large enough number of impulses to insure the release of relay I2 I of trunk circuit 49 while relay IZ-is operated "during the responseofrelayl I9to this train of impulses.

The release of relay I2I closes the circuit for energizing the lower winding of'relayi'i," thereby partially operating relay 51. When relay iZ l-releases at the end'of theprefix digit train, the

upper winding of relay 57 is energized to'complete' the-operation of this relay." The operation of-relacki'DBJ {so that in all'cases, the *operator keys on1y"=th'esdi'rectory' number1.:to extend connections,

tosubscribersin'idial oftlfces :A,..B and C. When so modified; the"locking:circuit.of relay H9 ineludes a back'contact' of relay 292.in1parallel nected through the :inner'glower. fronticontact of relay' I19; upper backcontact ofirelay I85, con"- ductor I82,.IOWBIlOaCRTCOiItaCB'Of relay 292, conductorIBI and'aifrontlocntact ofrelay I89 to signaling? battery. Theioperation of relay I89 connects grounditoi'conductor I99 causing the op-' eration'zzof relaysr293 and 295. When the plug lay*5l closes a circuit for operating relay 99 and connects conductors 5i and- 92- to the right wind ings-of repeating-coil 59. The operation of relay 99 connects the left winding of relay 96 and resister '95 in series with front contacts of relays I94 andl 19 across the inner ends of the right windingsof repeating coil 59, thereby preparing the sclector 69 for operation responsive to the next train of-impulses received by relay 4 l9. is'-=then'"operated to select a trunk through which the'connection'to the called subscriber line can be completedyand the succeeding digits effect the completion of the desired connection. The aforementioned operation-of relay99 caused the release of relay I25, whereby ground was reconnected to conductor I3'I"to release relays I 35 and I9I in the toll -office-and thereby effectthe-lighting of the cord supervisory lamp in the manner hereinbefore described. When all of the digits have been transmitted irom the sender, relay i85 is released first; and then relays I99 and H5 are released in succession;- When the operator disconnects cord I99 from the dial-back jack DBJ, relays I93 and I62 are released. Thecord is, however, not'disconnected from jack OJ until the connection between the calling and ca11ed subscriber stations is to be released. When the calling subscriber answers,

relay 86 operates; Relay 89 closes circuits for operating'relays 39 and I25. Relay l25reccnnects signaling battery to conductor I31 to operate relay I in the toll ofiice 'and'thus extinguish thecord supervisory lamp; Relay B9 locks undercontrol of relay'I I 9. The'talking connection includes repeating coil 59, the right windings of coil 59 being connected through contacts of relay 5?, conductors 5i and 62 and selector 69 to the calling subscriber station and the left windings of coil 59 being connected through contacts of relay 64, conductors II and 12 and selector 79 to the called subscriber station. Relay I25 is under the control of both of relays 86-and- I99 so that relay I25 responds to flashing at either of the connected subscriber stations; and relay I25 transmits the flashing signal received by either of relays 89 or 199 to relay I45 to flash the cord supervisory lamp. Release is effected in the manner hereinbeiore described when theoperator disconnects cord I99 from jack OJ The selector 59 By inserting Fig. 4Aron line A--A of Fig. 4; the

' a circuit? forrop'erating' relay 292.

of a:cordisiinsertedini jack DBJ, a circuit is closed through'the sleeve'conductors of the cord and j ack for "operating-relay 29 I. of relay 29I disconnects. the talking conductors of jacksi OJ 'andiAJ from" the trunk TI and closes With both of relays3292 and 295 operated, the locking circuit .ofrelay': I79 is opened and relay I19 releases.

The operation of..relay,.292 opens the connection between .outgoingrsignaling, conductor i4! and signaling battery and '.connects -conductor I 41 to ground atitheiloweriront.contact.of relay 293. Thesoperationxof relay. 292. causes .the release of relay.293.; but relay: 293 is slow inreleasing so.as.

tozmaintainthe connection .of ground .to. conductor/I41 longenoughstmeffect .therelease of signaling relay I35 in dial.office A. When relay 293 releases, the outgoing; signaling conductor. I47 is disconnected from ground. and connected through-a.backzcontactx of .relay 293, a back contact of relay.294, .conductor .I8I, and a front con tact ofrelay I89sto signaling battery. The release of- :relay, 293 causes. the operation .of relay 299,-;relay.294 being;slow inoperating so as to maintainthe connection .of signaling battery to conductor. I4 longenoughto effect the reoperation:obsignalingrelay,I35in dial oflice A. The operatiou'of relay2294 connects outgoingsignalingggconductor I41 toground at the upper front contact ofrelay295 and causes the-release of relay; 295. Relay 295 is slow inreleasing so as to maintain the .connectionzof ground to signaling conductor. I4'I.lor1'g.enoughto effect the release of relay: l35-rinrdial. oflice A. The release of relay; 205-. disconnects ground. from. conductor I47 and reconnects :conductor I 41 through contacts of relays-i I9andzl85, conductor I92, a front contact of .relay; 292,. a lbackcontact. of .relay 293, a front contact .of relay; 294,: a: back. contact of relay.1295;: conductor:I8I and .afront contact of relay; I89 to'signaling .battery, whereby signaling relay,+l35 in the .dial Mice A is reoperated. Thus the described'operationsof relays29 I. to 295 have transmitted the prefix digit 2 over the composite signalingchannelto relay. I35 in dial oflice A. Inresponse to .this prefix digit, relay I21 of trunk circuit lie-is releasedlong enoughto effect the operation ofirelays 51'and-99as hereinbefore described; so as to prepareselector 99for response to the succeeding trainsofdigit impulses transmitted'whentthe toll operator keys. the directory number of the subscribers station withwhich connection'iszto be established; The aforemen-i ti'o'ned"rel'easei'ofirelays I I9 effects the connection of 'groundto link start conductor I 99 andwhena;

sender has been: connected to trunk circuit I 59,

The operation.

relays I64 and I15 are operated. The operator then keys the directory number, the sender registers and retransmits these digits, and relay I 81 repeats these digit impulses over the composite signaling circuit to relay I35 in dial ofiice A, all as hereinbefore described on dial-back or delayed calls. When the plug is disconnected from jack DBJ, relays 20 I 202 and 204 release in succession.

What is claimed is:

1. In a telephone system comprising an operators position, a dial ofiice and trunks, one of said trunks interconnecting said dial ofilce and position, an outgoing jack and a dial-back jack at said position, a trunk circuit connecting one end of said one trunk to said jacks, a signal relay in said trunk circuit operatively responsive to signals incoming over said trunk from said dial ofiice, a key set at said position, cords for connecting either of said jacks with said key set, register senders, means effective upon connection of a cord to either of said jacks to connect a register sender to said trunk circuit, means in said register sender for registering digits under the control of said key set, means comprising said register sender and trunk circuit for transmitting digit impulses over said trunk, a control relay in said trunk circuit, means for operating said control relay responsive to operation of said signal relay, relay means in said sender circuit rendered effective by the operation of said control relay to prevent the transmission of impulses over said trunk, and means comprising a relay operated upon connection of a cord to said dial-back jack for preventing the operation of said control relay thereby to enable the transmission of impulses over said trunk while said signal relay is operated.

2. In a telephone system, a dial ofiice and a manual oflice comprising an operator position, a trunk between said ofiices, a first two-way trunk circuit associated with said trunk in said dial ofiice and a second two-way trunk circuitassociated with said trunk in said manual office, subscriber lines in said dial ofiice, means comprising said trunk and two-way trunk circuits for connecting a calling line to said position, an answering jack and a dial-back jack for said second trunk circuit, means including a cord at said position and said answering jack for answering calls incoming over said trunk, a selector switch associated with said first two-Way trunk circuit, means comprising a cord at said position and said dial-back jack for transmitting a train of digit impulses over said trunk to control the operation of said selector, means in said second trunk circuit automatically efiective responsive to the connection of a cord to said dial-back jack for transmitting signal impulses for a predetermined prefix digit over said trunk to said first trunk circuit, and means in said first trunk circuit responsive to said prefix digit impulses for operatively connecting said selector to said first trunk circuit.

3. In a telephone system comprising a manual oilice and first and second dial offices, a first trunk and a second trunk, said first trunk interconnecting said first and second dial ofiices, said second trunk interconnecting said second dial ofiice and said manual ofiice, an operator position in said manual office, subscriber lines in each of said dial ofiices, a first two-way trunk circuit terminating said second trunk in said second dial ofiice, and a second two-way trunk circuit terminating said second trunk in said manual office, means comprising automatic. switching means in said first dial ofilce for connecting a calling line therein to said first trunk, means comprising automatic switching means in said second dial oflice for connecting a calling line therein to said first two-way trunk circuit, means comprising said first trunk and said second trunk for at times connecting a calling line in said first dial oirlce to said operator position, means comprising said second trunk for at times connecting a calling line in said second dial ofiice to said operator position, means comprising an answering jack and a cord at said operator position for answering calls incoming over said second trunk to the manual Office, a key set at said operator position, a key set sender, outgoing and dial-back jacks for said second trunk circuit, means comprising a cord and either an outgoing or a dialback jack associated with said trunk circuit for connecting said key set to said sender, means in said sender controlled by said key set for registering the digits of the directory number of any subscriber in said dial oifices, means in said sender and second trunk circuits for transmitting digit impulses corresponding to said registered digits over said second trunk to said first trunk circuit, a selector in said second dial offlce, means in said second two-way trunk circuit automatically effective only upon connectionof a cord to said dial-back jack for transmitting a predetermined prefix digit over said trunk to said first two-way trunk circuit, and means in said first two-Way trunk circuit responsive to the prefix digit for preparing said selector for response to the train of impulses corresponding to the first digit of a called subscribers number.

4. In a multioflice telephone system, an operator position, a two-way trunk extending from said position to a dial oifice, a trunk circuit connected to one end of said trunk comprising an outgoing jack and a dial-back jack at said position, means comprising a signal relay in said trunk circuit responsive to signals incoming over said trunk from said dial office, means associated with said trunk circuit for sending selective signals over said trunk to said dial office, circuit means comprising said outgoing jack and a control relay in said trunk circuit operatively energized while said signal relay is operated for preventing the transmission of selective signals over said trunk to said dial office, and circuit means including said dial-back jack for preventing the operation of said control relay thereby rendering said signal sending means effective to transmit selective signals over said trunk to said dial ofiice while said signal relay is operated.

SEWELL W. ALLISON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,979,020 Whitney Oct. 30, 1934 2,073,752 Norton Mar. 16, 1937 2,105,012 Saunders Jan. 11, 1938 2,208,765 King July 23, 1940 2,230,052 Crocker Jan. 28, 1941 2,261,485 Peterson Nov. 4, 1941 2,268,397 Hersey Dec. 30, 1941 2,302,587 Ulrich Nov. 17, 1942 2,333,485 Molnar Nov. 2, 1943 2,337,433 Walsh Dec. 21, 1943 2,340,554 Peterson Feb. 1, 1944 2,433,359 Gohorel Dec. 30, 1947 

